op cohning



Aug. `2s, 1923.

E. PASCUCCI REFLECTOR Filed Nov. 29 1920 E. Pasczczl,

INVENTOR TTORNEY Patented Aug. 28, 1923.

UNITED STATES PATENT oFFicE.

EMILIO PASCUCCI, Ol? CORNING. NEW YORK. ....SSIGTOR TO CORNING GLASS WORKS, OF CORNNG, NEW YORK, A COREORATION OF NBV? YORK.

REFLECTOR.

Application led November 29, 1920.

To (dit rfi/710m` 'it may concern Be it known that l, Ennio Pascucci, a citizen ot the llnited States oi ftnieriea.. and a resident ot the ci ty oit Corning, county ot tenben, State of Nee.' York, have invented certain new and uselul lniprovenients in Retlcctors, of which the 'tollen/ingr` is a spec-itication.

This invention has tor its object to provide a reflector in which spherical aberration bv reflection is reduced or entirely eliminated, and this without the difficulties which allowed the Yformation ot parabolic surfaces. For this purpose there is combined, in a. sina'le strutture, a concave retleeting surface haring spherical aberration. and a retracting body overcoming' such aberration. This is accomplished by the use ot a concavo-convex transparent element, the it'aces ot which are so shaped that light falling on the tront concave tace thereot and passingr therethrough, atter reflection troni the convex rear Vtace (which may be suitably coated) and after again issuing Ytroni the front tace, will be directed, due to retraction, as though spherical aberration was not. present. Such a structure is therefore a, katadioptric element. h

lleterring to the accompanying drawings in which iorrespondinan,v parts are designated by corresponding` marks of reference,-

Figure l, is a central longitudinal section through a reflector embodyingT this invention.

Figure 2, is a diagram illustrating in a quantitative manner, a set ot' curvatures which are suggested as cnilodying` a specitic type thereof.

As is well known, only that part ot a spherical niirror located within a 'feu' de grees about its peripheral axis is capable ot reflecting' in a parallel beam light en'lamlting from the principal tocal point ot such portion, rays 'troni such point 'Falling` on the mirror outside ot such portion being convergently reflected. It is also known that rays troni a liejht source located behind the principal focal point ot' a spherical mirror are in the absence of spherical aberration di- Vcrg'ently reflected. In the present invention the divergence. due to a source located behind the principal 'focal point oit the central portion of the mirror fis utilized to con Serial No. 427,095.

rect, `for a. `given and selected zone ot the mirror intermedia-te ot its center and its periphery, the convergence due to spherical aberration, so that While portions ot the mirror inside ot such '/.one tend to project a divergent bean, and portions outside of the zone a convergent beam.y the reflection ot the two last named portions are corrected by retraction, due to the radial cross section 2given to the mirror by the contour of its front and rear taces.

Referring: to the embodiment shown in the drawings, the rear corer tace L of the light projectingelement A (which niay be o'i transparent glass) is spherical, being` struck from the center o1, While the front concave .tace Z is non-spherical, successive parts thoreot on each side ot the principal axis nflah beingstruck from the points 1, b2,

'53. and o, which are so located that the light projecting element A gradually increases in thic ess on va radial line trom a circle concentrlc with the principal axis and interinodiate ot it and the peripheral 'liront ed ee-o t the element` the element in etl'ect beingY thus composed oi inner and outer annular prisnioids, whose bases are reversed in respect to each other, the rear Ytace ot each prisinoid being spherical. and the forward `tace ot which is nonsspherical.

The rear 'tace (L is ,given a reliecting coating` in any proper and known manner, as by Silvering.

The central portion ot' the tront tace may, .it desired, and as shown. be termed flat inasmuch as in practice. the greater portion ot this is out awayat c to receive the socket of the lamp employed as the liejht source.

A suitable light source D is located behind the principal tocal point ot the non-central portion o l the spherical inirror .torined by* the coated rear tace. This location is such that were the 'trout and rear faces o'l the elenient A parallel to each other, light| `falling on the element at a point near its periphery would, say at m1, due to reflection and refraction, be projected convex'grently in rc- 'spect to the principal axis` this being due to spherical aberration. Under the saine supposition, a ray falling); on the front tace ot the element A at a point nearer the prin cipal axis. say at nl, will be reflected and rcracted divergently in respect to the principal axis. lt will be noted that the spherical aberration of' rays reflected troni a spherical mirror at a. point correspondingto 'nl is, due to the location of such point, much less than that of the rays reflected from a point such as mi, so that as to the last named pointthe divergence, clue to the location of the light source, overcomes the convergence due to spherical aberration, It Will he further noted that under the supposition niade,` refraction is not effective in diverting the direction of the rays.

lf, however, the light projectingl element A has not parallel front and rear faces, but has at the point m1 the cross section of' prisnioichivith the hase outward, and at nl thatofva prisrnoid with the base inward, the path of the rays is modified. As shown by the dashed lines MM1'--l\l2--M3 on the lowerhalf of Figure 1,'the refraction of the outer prisin tends to draw the ray impinging on a part of the front face correspondinp, to the point m, before considered, intoy par` yallelisniivith the ,principal axis, While due to the action of' the inner prisin, the reverse is true of a ray falling on a point N corresponding' to the point al, as is shown by the dashed line D-N--N,1--N2--l`\l3.

Rays falling onv the 'front face, immediately at the junction of the prismsare refracted towards the axis on entering the light projecting element, and in the reverse direction on leavingthe element. These refractions practically neutralize each other, so that theV direction of the rays after leavin@ theelenient is determined solely by the re ecting face. The light source is thus lo-` catedsubstantially at the principal focal point-of that part of the reflecting face Whichis located behind the circle separatingY the outer and inner prisnioids.

By selecting proper locations for the centers and proper lengths for the radii of curvature of the several faces and parts thereof, a iniiror of lshort focal length and large area may be constructed which will project 1a substantially parallel beam, and this Without the difliculties attending `the use inesfiio of parabolic surfaces which are diflicnlt lo obtain in a polished condition in glass.

The construction described has the adi'antage that the reflectingsurface is a convex one and is spherical, and is hence easy to polish by machinery. On the other hand, slight irres rularitiesv on the concare,y or reiacting surface, are not greatly detrimental to accuracy, and such surface may therefore, if desired, he left in the state it cornes troni the inold, or be inerely firepolished, but l do not in this appliration'claiin a light projector having` such polished and ,silvored rear surface, and a pressed "Forward surface.y as that foiins the subject-matter of another application filed on the 22nd day of De ceinber, 1922, by Henry Flielps Gage;

ln Figure 2 is shown :i quantitativo e1:-

ainple of a light projecting element falling` Within this invention, the refractive index of the glass being 1.53. lt will be understood, however, that this example is given merely to aidin the understanding of hov,7 the saine inay be eonstructechand not as a limitation on the scope.`

Having thus described invention, l dey Clare that Whatk I clairn is:

.axis and its periphery, with a lips-ht source located substantially at the principal focal point of that part of the reflecting face corresponding to such circle.y

2. The combination of a katadioptric light projecting;` element having' a sperical reflect ing rear face, aV concave retracting; front tace so struck that the clement- `gradually thickens on both sides of a circle intermediate ot its principal axis and its periphery, with a light source located at substantially the principal.

focal point of that part of the reflecting;` face corresponding to such circle.

EMILIO PASGUCCI. 

